Lufthansa flights hit as crew start strike

German airline Lufthansa has cancelled hundreds of flights and warned of more disruption on the weekend after a cabin crew union started a series of walkouts that could become the longest-ever strike at the carrier.

On the first day of a planned week of protest over failed pension talks, flight attendants were instructed to strike at Frankfurt, Lufthansa's biggest hub, and Duesseldorf on Friday afternoon and evening, affecting about 37,500 passengers.

That will be followed by walkouts on short-haul flights from Frankfurt and all flights from Duesseldorf for most of Saturday, the UFO union announced.

According to Lufthansa, that will result in about 520 short-haul flights being cancelled, affecting 58,000 passengers.

The walkout comes after Lufthansa and the union failed to reach an agreement in a long-running row over early retirement benefits and pensions.

Lufthansa is trying to negotiate with various staff groups to bring down pension costs as part of a savings drive to allow it to compete better with low-cost rivals and wealthy Gulf carriers.

Should Lufthansa management not make concessions, the union will carry out a threat to stage more walkouts until November 13, it said.

Equinet analyst Jochen Rothenbacher said strike costs could total 20 million euros ($A30.47 million) a day, depending on the number of cancellations, giving a total of around 140 million euros should the union strike on seven days, as threatened.

Strikes by pilots have already cost Lufthansa 130 million euros so far this year.